People walk away from Brussels airport after explosions rocked the facility in Brussels, Belgium Tuesday March 22, 2016. Explosions rocked the Brussels airport and the subway system Tuesday, just days after the main suspect in the November Paris attacks was arrested in the city, police said. (AP Photo/Geert Vanden Wijngaert)

BRUSSELS (AP) — Explosions, at least one likely caused by a suicide bomber, rocked the Brussels airport and subway system Tuesday, prompting a lockdown of the Belgian capital and heightened security across Europe. At least 28 people were reported dead.

A spokesman for the Brussels Metro said 15 people were killed and 55 injured in an explosion on a train, and Belgian media reported at least 13 dead in two explosions at the airport, with many others injured.

Belgium raised its terror alert to the highest level, diverting planes and trains and ordering people to stay where they were. Airports across Europe immediately tightened security.

“We are at war,” French Prime Minister Manuel Valls said after a crisis meeting called by the French president. “We have been subjected for the last few months in Europe to acts of war.”

European security officials have been bracing for a major attack for weeks, and warned that the Islamic State group was actively preparing to strike. The arrest Friday of a key suspect in the November attacks in Paris heightened those fears, as investigators said many more people were involved than originally thought, and that some are still on the loose.

There was no immediate claim of responsibility for Tuesday’s attacks, and Belgian Prime Minister Charles Michel said there was no immediate evidence linking key Paris suspect Salah Abdeslam to them. After his arrest Friday, Abdeslam told authorities he had created a new network and was planning new attacks.

Belgian media reported that 13 people were killed at the airport, where two explosions splattered blood across the departure lounge and collapsed the ceiling. The explosions hit during the busy morning rush. Smoke was seen billowing out of the terminal.

In this photo provided by Georgian Public Broadcaster and photographed by Ketevan Kardava two women wounded in Brussels Airport in Brussels, Belgium, after explosions were heard Tuesday, March 22, 2016. A developing situation left at least one person and possibly more dead in explosions that ripped through the departure hall at Brussels airport Tuesday, police said. All flights were canceled, arriving planes were being diverted and Belgium’s terror alert level was raised to maximum, officials said. (Ketevan Kardava/ Georgian Public Broadcaster via AP)

Anthony Deloos, an airport worker for Swissport, which handles check-in and baggage services, said the first explosion took place near the Swissport counters where customers pay for overweight baggage. He and a colleague said the second blast hit near the Starbucks cafe.

“We heard a big explosion. It’s like when you’re in a party and suddenly your hearing goes out, from like a big noise,” Deloos said, adding that shredded paper floated through the air as a colleague told him to run.

“I jumped into a luggage chute to be safe,” he said.

Tom De Doncker, 21, check-in agent intern, was near the site of the second explosion.

“I saw a soldier pulling away a body,” he said. “It felt like I was hit too” from the concussion of the blast.

Zach Mouzoun, who arrived on a flight from Geneva about 10 minutes before the first blast, told BFM television that the second, louder explosion brought down ceilings and ruptured pipes, mixing water with victims’ blood.

Near the entrance to Brussels’ Maelbeek subway station, not far from the headquarters of the European Union, rescue workers set up a makeshift medical treatment center in a pub. Dazed and shocked morning commuters streamed from the metro entrances as police tried to set up a security cordon.

“The Metro was leaving Maelbeek station for Schuman when there was a really loud explosion,” said Alexandre Brans, 32, wiping blood from his face. “It was panic everywhere. There were a lot of people in the Metro.”

Francoise Ledune, a spokeswoman for the Brussels Metro, said on BFM television there appeared to have been just one explosion on the subway in a car that was stopped at Maelbeek. Spokesman Guy Sablon said 15 were killed and 55 injured in that attack.

At the airport, passengers fled as quickly as they could.

Amateur video shown on France’s i-Tele television showed passengers including a child running with a backpack dashing out of the terminal in different directions as they tugged luggage. Another image showed a security officer patrolling inside a hall with blown-out paneling and what appeared to be ceiling insulation covering the floor.

Marc Noel, 63, was about to board a Delta flight to Atlanta, to return to his home in Raleigh, North Carolina. A Belgian native, Noel says he was in an airport shop buying automobile magazines when the first explosion occurred 50 yards away.

“People were crying, shouting, children. It was a horrible experience,” he told AP. He said his decision to shop might have saved his life. “I would probably have been in that place when the bomb went off.”

With three runways in the shape of a “Z,” the airport connects Europe’s capital to 226 destinations around the world and handled nearly 23.5 million passengers in 2015.

Passengers were led onto the tarmac and the crisis center urged people not to come to the airport.

Authorities told people in Brussels to stay where they were, bringing the city to a standstill. Airport security was also tightened in Paris, London and other European cities.

In Paris, France’s top security official said the country was immediately reinforcing security at airports, train stations and metros.

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Associated Press Writers Raf Casert in Brussels and Angela Charlton and Lori Hinnant in Paris contributed to this report.